Current control circuit



May 7, 1957 w. H. BLISS 2,791,719

CURRENT CONTROL. CIRCUIT Filed March 25, 1954 2 Sheets-Sheet 1 I. L240 16 a 16 CURREN T I U TIL IZA T/ON DEVICE All-l V0]. TAGE REFERENCE 9 PO! N 1' STABILlZ/NG jg 4522 1 7 AMA/Flaw DEFLECTION COIL 11001! INVENTOR.

Z15 7.2. WARREN H. Buss ATTORNEY 2 Sheets-Sheet 2 Filed March 23, 1954 INVENTOR. WARREN ILBmss gm @EMIEE wQN 4 T W H .w\\ P I Il 11 TTORNE I United States Patent Oflice 2,791,719 Patented May 7, 1957 CURRENT CONTROL CIRCUIT Warren H. Bliss, Princeton, N. J., assignor to Radio Corporation of America, a Delaware corporation Application March 23, 1954, Serial No. 418,025

11 Claims. (Cl. 315-47) This invention relates to arrangements for providing a current in response to an input signal, and more particularly to novel circuits which provide increments of current in response to an input signal.

Arrangements have been proposed for producing intelligible configurations of alphabetical and numerical characters by means of an electron beam. Means may be provided for selectively producing electron beam images of particular alphabetical and numerical characters. Each of the images is then projected to a preselected position on a fluorescent screen. The image on the fluorescent screen may be recorded by any means for converting a light image to a permanent image such as photography. This technique may be used to produce printed matter at very high speed from a coded input signal. It may be used advantageously in a number of related fields including high speed electronic type setting and for recording of coded information derived from high speed computers.

To produce an electron beam image of a selected character, and to position this image in a preselected position on a fluorescent screen may require precise deflection of an electron beam in response to a coded input signal. The well known magnetic deflection method may be used. Using this method the current input to the deflection coils must, therefore, precisely correspond to this coded input signal. The present invention teaches how such a precisely controlled current maybe provided.

An object of this invention is to provide a precisely regulated current supply which is independent of fluctuation in voltage.

Another object is to provide a current which precisely corresponds to an input signal which may have code significance.

Still another object of this invention is to provide a means for supplying precise increments of current over a series of discrete steps in response to an input signal which may have code significance.

A further object is to provide a stabilized self-balancing current source which maintains its self-balancing characteristic over a range of current requirements.

Still a further object is to providea stabilized source of current which provides precisely determined values of current corresponding to variable current or variable potential values of input.

Still a further object is to provide aprecisely regulated current source which provides precise increments of current in discrete steps in response to an input having binary significance.

Still a further object is to provide a novel precisely regulated current source for supplying discrete increments of current over a range including both positive and negative values.

Still a further object is to provide a precisely regulated source of deflection current for an electron beam having the described characteristics.

Still a further object is to provide a novel centering system for a deflected electron beam.

Still a further object is to provide a centering control for an electron beam deflection currentsource having the described characteristics.

Still a further object is to provide a means for providing high speed fiyback for an electron beam deflection cur* rent source having the described characteristics.

An illustrative example of a circuit, which practices the present invention to fulfill these objects, provides cur rent increments for the deflection coils which may be used in a high speed electronic type setting device.

The deflection current may besupplied and controlled through the output circuit of a current amplifier. A grid controlled triode may be used as the current controlling and supplying amplifier. This triode Will be referred to hereafter as the current controlling triode. The current control triode draws its input current from a positive potential source. A bus is provided for maintaining a predetermined potential for governing the current flow through the current control triode. It may be considered to be a voltage reference point of the system. A signal indicating a change in bus potential is fed to the grid of the current control triode through a feedback amplifier. If the potential on the bus should rise due to a variation in current flow through the current control tube, the feedback amplifier produces an amplified voltage drop on the control grid of the current control tube. This drop reduces the current flowing through the current control tube. This action reduces the bus voltage back to its stabilized value maintaining a closely regulated current flowing through the control tube.

The condition of balance of the bus may be changed by varying the applied input voltage or input current in discrete steps. A series of electronic switches may be used to provide a number of discrete steps of current to the stabilized bus. The bus stabilizes at essentially the same potential for each increment of input current. In response to these input current increments, the current control tube provides corresponding increments of output current. The deflection current through the control tube, therefore, corresponds to the variation in input signal. Various increments of input signal current may be provided by means of various precision resistor combinations. These input current increments produce corresponding deflection current increments.

To provide positive and negative values of deflection current, the current control triode may be replaced by a pair of cascade connected triodes. The deflection coil is connected from the common terminal of these cascaded triodes to ground. The high gain feedback amplifier directly controls the grid of one triode and indirectly controls the grid of the other triode through a phase inverter. According to the distribution of current flow through :each of the triodes, any given value of current may be supplied to the deflection coil ranging from a maximum positive to a maximum negative value.

To provide a centering control, compensating current may be supplied as input to the feedback amplifier. This provides a means for setting the deflection coil current to any preselected value for zero signal input.

For high speed operation, it may be desirable to deflect the beam more quickly in the return direction than it is deflected in the forward direction. Additional energy may be supplied to deflect the beam more rapidly in the return direction. An amplified positive pulse derived from the phase inverter at the instant of each return is amplified and coupled into the deflection coils to help overcome the inertia of their inductance. This pulse may be coupled by means of a capacitor into the yoke coils along with the normal deflection current.

Other objects and advantages of the present invention will become apparent to one skilled in the art:from arcad- :ing of the following specification in conjunction with the accompanying drawing of an illustrative example of the present invention in which:

Fig. 1 is a schematic diagram of a circuit embodying several of the novel features taught by this invention,

Fig. 2. is a schematic diagram of a circuit embodying additional features of novelty and,

Fig. 3 is a more detailed schematic diagram embodying the features of novelty shown in Fig. 2 along with additional novel features.

In Fig. 1 a circuit is shown for producing precise and discrete steps of current which may be utilized in a char acter selecting or positioning cathode ray tube deflection circuit. The cathode of a current control tube which may be an amplifier vacuum tube of the 6V6 type is con nected through a resistor 62 to a stabilizing bus 12. The cathode of the current control tube is also connected to ground through a resistor 14. A current utilization device 16 which may be the deflection coils of a character selecting or positioning cathode ray tube is connected in the plate circuit of the current control tube. The grid potential of the control tube is regulated from an amplifier which may be the three-stage feedback amplifier 13.

The feedback amplifier is made up of three stages. The first stage may incorporate a dual triode 20 which, for example, may be a tube of the 61 6 type with both sections connected in parallel. The output of the first stage is coupled to the grid of triode 22. Triode 22 may be onehalf of a dual triode 24 which may be of the 12AX7 type. The output from triode 22 is connected to the grid of the second half 26 of the dual triode 24. The output from the last stage of the feedback amplifier 18 is connected to the control grid of the current control tube 10. The cathode of the first stage of the feedback amplifier is connected to ground.

Resistors 28, 30 and 32 connect each of the plate circuits of the amplifier tubes to a positive source of voltage. The plate circuit of second stage amplifier tube 22 is coupled to the grid of third stage amplifier tube 26 through resistor 36. The plate circuit of the third amplifier tube is coupled to the grid of current control tube 10 through resistor 38. The cathode of the tube 22 of the feedback amplifier is positively biased by means of potentiometer 40 and resistor 34 connected to the positive bus. P0- tentiometer 40 provides an indirect means for adjusting the stabilized potential in the bus 12.

A current input signal varying in discrete steps is supplied to the bus or voltage reference point 12 by a series of electronic switches having binary sequence significance. The input may be also supplied, for example, by any source of variable potential or current. In this illustrative circuit precise increments of current are supplied through the electronic switches in order to produce corresponding precise discrete current steps or increments for the deflection coil 16.

Three pentodes 42, 44 and 46 may have their plate circuits individually connected to the stabilizing bus 12. These pentodes may be of the 6AN5 type. The cathodes of the switching tubes 42, 44 and 46 are connected to a negative source of potential. The switch tubes are normally biased to cut off when switches S42, S44, and S46 in the grid circuits of the tubes are open. Normally these switch tubes are controlled by positive potentials from an electronic control system. The mechanical switch arrangement is introduced only for ease and clarity of presentation. The control grid of the switch tubes are connected respectively to a negative source of potential which may be 150 volts through resistors 48, 50 and 51. Screen potential for the switch tubes is provided by means of a potential divider consisting of resistors 58 and 60 connected from ground to a negative source of potential r allows a wide range of linear operation for the current control tube 10. The current control tube 10 is connected as a triode so that its plate and cathode currents may be identical.

A negative source of potential which may be volts is connected to bias the grid of the triode 26 of the feedback amplifier through resistor 65. This 150 volt negative source of potential also is connected to bias the control tube grid circuit through variable resistor 66 and fixed resistor 68. The variable resistor 66 is adjustable for allowing the amplifier to be adjusted for optimum performance. The cathodes of the feedback amplifier are connected to ground. 7 I

The bus 12 is arranged to stabilize in potential at a value slightly negative with respect to ground. The three stage triode feedback amplifier 18 maintains this preselected potential by controlling the amount of conduction through current control tube 10. If the potential on bus 12 rises slightly, this causes the first stage amplifier tube 20 to draw more plate current. This in turn lowers the potential on the control grid of triode 22. This decreases current flow through triode 22 which in turn decreases the output plate potential of direct grid coupled triode 26. The amplified original voltage change undergone by bus 12 is applied from the last stage of the feedback amplifier to the control grid of current control tube 10. This reduces the current flowing from the cathode circuit of tube 10 to ground through resistor 14. Since the bus 12 is connected to the cathode circuit of current control tube 10 through another resistor 62, the voltage or potential imposed on the bus 12 is thereby returned to its stabilized preselected potential.

The switch tubes 42, 44 and 46 are normally biased to cut-off when the associated switches S42, S44 and S46 respectively are open. When switch S46 is closed, the control grid of tube 46 is brought up to cathode potential and a conduction path is established from ground to the -l02 volt supply through resistors 14, 62 and 56. Since the anode to cathode impedance of tube or pentode 46 is very small compared to the resistance of resistor 56, the current through this conduction path is effectively dependent only on the value of resistor 56. Resistors 52', 54 and 56 may be precision resistors so that accurately adjusted current steps may be provided when they are selectively connected into the input circuit. I

Switch tubes or pentodes 42 and 44 operate in a similar manner when their associated switches S42 and S44 respectively are closed. The associated plate precision resistors 52 and 54 respectively, however, are of difierent values of resistance from that of resistor 56. For example, resistor 56 may have a resistance of 96,000 ohms. Resistor 54 may have a resistance of 48,000 ohms and resistor 52 may have a resistance of 24,000 ohms. With this proposed binary arrangement, the current drawn by tubes 46, 44, and 42 are respectively one current unit, two current units and four current units.

At the instant when switch S46 is closed, there is a momentary drop in potential on bus 12 because of the one unit of current which flows through resistor 56. Immediately after this drop of potential occurs, the feedback through amplifier 18 to the control grid of current control tube 10 causes the current control tube 10 to draw an additional increment of current through its cathode resistor 14. This raises the potential of the bus 12 once again to its stabilized or regulated value. This balanced condition will be maintained as long as the one unit of current flows through the switch tube 46.

When switch S44 is closed, tube 10 is actuated in the same manner as described previously through the feedback amplifier to draw an additional increment of current which is double the value of the initial increment.

When switch S42 is closed, tube 10 must increase its cunrent flow by four times the initial increment in order .to stabilizethe bus 12. Resistor 62 has a resistance many times greater than that of resistor 14. The current, theredesignated as point 94.

fore, drawn by tube may beseveral times greater than the total of currents drawn through precision resistors 52, 54 and 56. A relatively small flow of current through the switching tubes may, therefore, precisely control a much larger current. This controlled current is provided to a current utilizing device 16 which may be the character selecting or positioning deflection coil of a cathode ray tube.

The currents drawn through resistors 52, 54 and 56 by closure of their associated switches are mutually independent. The relatively large current drawn through current control tube 10 is, therefore, proportional to the sum of the currents through precision resistors 52, 54 and 56. By closing different combinations of the three switches, the current drawn through tube 10 may be controlled accurately to any one of eight dlifferent stabilized current steps which may range from zero current units to 7 current units. A multiplicity of relatively high current steps are therefore precisely controlled by switching different combinations of these precision resistors with with relatively low current flow through them. In general, if it switches are used, this type of input circuit controls 2 steps of current. This is therefore basically a binary to analogue conversion.

Other types of input devices may be used in conjunction with the feedback amplifier and current control tube. They may provide an input signal which feeds in various discrete potential or current values which control the amplitude of stabilized current increments to be supplied to the current utilization device. Switches S42, S44 and S48 may be electronic devices controlled by photocells which are actuated by light penetrating the perforations in a tape which, for example, may be perforated in teletype code. The stabilized current provided by the current control tube may be utilized in other applications requiring a stabilized current, for example, in a precision deflection circuit for a color television scanner or receiver.

In Fig. 2, is shown a simplified schematic diagram of a device which utilizes features of the device shown in Fig. 1 together with additional novel features. This device provides means for controlling the current supplied to a utilization device over a range of currents which includes both positive and negative current values. This device is well adapted for controlling the positioning deflection current for a character selecting cathode ray tube.

A current utilization device 70 which may be a character selecting or positioning deflection coil of a cathode ray tube is connected from the midpoint of cascaded current control triodes 72 and 74 to ground through a small variable resistor 76. The control grid of triode 72 is supplied by the output of a high gain feedback amplifier 78. The amplifier 7 8 output is connected also through a phase inverter 80 to the control grid of the other triode 74. A phase inverted input is thereby providedto the cascaded triodes. The cascaded tubes are connected from a positive source of potential which may be +100 volts to a negative source of potential which may be 100 volts.

A stabilizing bus 92 corresponding to bus 12 in Fig. l is connected to a positive source of potential which may be +250 volts through resistor 82. The bus 92 is connected to ground through resistor 84 and variable resistor 76. A negative potential which may be -100 volts is connected to the bus 92 through series connected resisters 86 and 88. An input terminal 90 is provided between resistors 86 and 88. The junction point between the deflection coil '70 and variable resistor 76 may be feedback amplifier 78.

Current control triodes 72 and 74 control the flow of current into or out of the deflection coil by virtue of their inverted input relationship and their connection across a positive and a negative potential source. When triode Bus 92 provides the input to.

-72 :is conducting and triode 74 is almostcut off, ,a positive flow of current flows through the deflectioncoil 70. When triode 72 is almost out ofl? and triode 74 is conducting, a negative flow of current flows through the deflection coil 70. When equal currents flow through the current control triodes 72 and 74 no current flows through the deflection coil. .By controlling the potential supplied to the grids of the ditferentially acting current control triodes, the deflection coil may therefor be set to any current value over a range extending from a maximum positive value to a maximum negative value.

The high gain feedback amplifier 78 supplies the potentialto the control grids of the current control triodes. It supplies a potential directly to the grid of triode 72 and it supplies a potential indirectly to the gridoftriode 74 through phase inverter 80. This inverted connection provides a means for swinging the potential of the grid of triode 72 in the opposite direction to the potential variation applied to triode 72. A variation in potential in the output of the amplifier 78 will, therefore, cause the current through deflection coil 70 to vary through a range covering both positive and negative current values.

The amplifier 78 stabilizes the deflection coil current in a manner similar to the function of the three stage feedback amplifier shown in Fig. l. The output current from the deflection coil 70 flows to ground through a small resistor 76. This current flow develops a drop in potential at point 94. When no input signal is applied at the input terminal 90, the effect of the potential at point 94 is carried through resistor 84 to the stabilizing bus 92. The junction of resistors 82, 84, 88 and high feedback amplifier 78 may be designated as point 91.

This point may be described as a voltage referencepoint of the circuit which is maintained at a-substantially constant potential along with the bus 92. The high gain amplifier 78 supplies an amplified signal to readjust the current flow through the current control tubes. A stabilized current flow is, therefore, maintained through-the deflection coil 70 at any given input potential. This function is similar to the potential stabilization of the bus 12 as previously discussed in connection with Fig. 1.

if the +100 volt plate supply to triode 72 were, for example, slightly increased because of an inherent line voltage fluctuation, the current through the deflection coil will start to increase. The potentials at bus 92 and point 94 would therefore tencl'to increase. The variation in the input to feedback amplifier 78 would in turn cause it to decrease the control grid voltage of triode 72. This would lower the deflection coil current back to its original stabilized value. The control grid potential of triode 74 would be increased slightly through the phase inverter to assist in this stabilizing action.

An input of voltage or current applied at input terminal 90 may be used to control the deflection current over a range of current values. The input signal may be supplied by a binary configuration of electronic switches as shown in Fig. l or it may be produced by other signals such as the common sawtooth wave. When a positive potential is applied at the input terminal 90, bus 92 will tend to become more positive. The circuit however will instantly stabilize itself to the original stabilized condition by producing a suitable altered current flow through the deflection coil 70. The change in voltage across resistor 84 produced by this input signal will be opposed by a corresponding change in voltage across resistor 76 produced by the change in current through the deflection coil 70. As the applied input voltage or current changes, the current through the deflection coil precisely follows the variations in input signal.

Resistor 82 may be made adjustable to be used as a centering control. This enables the deflection coil current to be set at any preselected current value when there is no input signal applied. The variable resistor '76 may be used as a deflection current amplitude control. The lower the resistance of resistor '76, the greater the current through the deflection coil must be in order to stabilize the circuit for any given input signal.

In Fig. 3 is shown a detailed schematic diagram of a circuit including the features shown in Fig. 2, together with details of a centering control and a quick acting flyback arrangement. The high gain feedback amplifier is shown as a three stage vacuum tube amplifier 100. A high gain feedback amplifier is made up of three stages utilizing parallel connected dual triode 106 which may be of the 616 type, as the first stage. Triode 108 which may be one-half of a dual triode 110 of the 12AX7 type is used as the second stage. Triode 112, which may be the other half of the dual triode 110, is used as the third and final stage of the feedback amplifier.

The feedback amplifier is connected to function in a similar manner to the feedback amplifiers described in Figs. 1 and 2. A dual triode 114 which may be of the 6AS7-G type with both sections in parallel is connected in a similar manner to the current control triode 72 shown in Fig. 2. Dual triode 116 which also may be of the 6AS7-G type with both sections in parallel is also connected to function in a similar manner to the current control triode 74 in Fig. 2. Another triode 118 whose grid is connected in the plate circuit of the feedback amplifier final stage to provide phase inversion for the control grid of negative potential supplying current control triode 116. The cathode of the second stage feedback amplifier tube 108 is connected to the variable tap of potentiometer 130 which is used in connection with resistor 144 to adjust for optimum amplifier performance in a similar manner to resistors 40 and 34 in Fig. l. The plate circuits of the various stages of the feedback amplifier are connected to points in a potential line which may be maintained at +250 volts through resistors 136, 138, 140 and 142. The cathodes of the various stages of the feedback amplifier are connected to ground. The output of the second stage amplifier tube 108 is coupled to the output of the 3rd amplifier stage tube 112 through resistor 146. Capacitor 148 is connected from grid to plate of triode 112 to prevent oscillations. A negative source of potential which may be 210 volts is connected to bias the grid of the final amplifier stage tube 112 through grid resistor 150. The 210 volt source of potential also biases the grids of dual triode 114 through grid resistor 152. The output of the final stage amplifier tube 112 is connected to the grid circuit of current control triode 114 through resistor 154. The centering control is provided by the variable tap on resistor 120. Resistor 120 is connected in series with resistors 132 and 134 from a negative source of potential which may be l volts to a positive source of potential which may be +250 volts. A portion of the output of the feedback amplifier is connected to the grid of the phase inverter tube 118 from the junction of resistors 140 and 142 through resistor 156. A positive source of potential for the positive deflection current control triode 114 which may be +100 volts is connected to the plate circuit of the phase inverter 118. The input to a pentode 122 is capacitively coupled to the phase inverter tube 118 output circuit through capacitor 124. The plate circuit of this pentode is coupled to the deflection coil through the capacitor 126. The plate circuit of phase inverter tube 118 is con- 'nected to the grid circuit of negative current control tube 116 through resistor 164. A negative source of potential which may be 2l0 volts is connected between resistors 160 and 162 for biasing the grids of tubes 116 and 118. A negative source of potential which may be +100 volts is connected to the cathode circuit of current control tube Resistors 166 and 168 are connected as a potential divider between negative sources'of potential which may be +210 volts and -l00 volts to provide suitable control grid bias for pentode 122. A positive source of potential, which may be +120 volts is applied to the first screen of pentode 122., A positive source of potential, which may be +250 volts, is applied to the plate of, pentode 122 through a resistor 170.

The current deflection coil 172 is connected between the cascaded current control triodes 114 and 116 to ground through variable resistor 128. Variable resistorv 128 is connected to the deflection coil 172 to control the amplitude of the deflection current in a similar manner to that of resistor 76 in Fig. 2. An input signal terminal 182 is provided at a point between resistors 1'78 and which connect to the stabilizing bus 174 from a negative source of potential which may be l00 volts. Deflection coil 172 is connected to stabilizing bus 174 through resistor 176.

The feedback amplifier portion of the circuit operates in a similar manner to the feedback amplifier described in Fig. l. The cascade connected current control tri odes 114 and 116 operate to provide a stabilized current over a range from a positive to negative value in a manner similar to the current control triodes described in Fig. 2. A differentially controlled current is thereby provided for deflection coil 172. The type 6AS7G dual triodes with both sections connected in parallel may be used to give deflection currents as high as 250 milliamperes for the deflection coil.

An input signal may be provided at input terminal 182 to vary the deflection coil current over the allowable range. The differentially connected dual triodes or current control tubes 114 and 116 supply a stabilized current corresponding to each given value of input. A binary configuration of electronic switches similar to those described in Fig. 1 may be utilized as the input. The switch actuation for this binary configuration may be supplied by a photocell scanned tape having perforations corresponding to characters to be selected and reproduced.

Centering adjustment is provided by the variable tap of potentiometer 120, This tap is connected to the stabilizing bus 174- of the feedback amplifier so that the current flow through the deflection coils may be varied with no input signal imposed.

Phase inversion for the grid of the negative potential current control tube 116 is supplied by the triode 118. The phase inverter tube may be a single section of a type 12AU7 dual triode.

Pentode 122 helps in changing the deflection current when it is shifted from a positive to a negative value. This would, for example, speed up the return trace when a sawtooth input signal is provided. When this device is operating at a high speed, additional energy is supplied through this flyback circuit to help overcome the inertia of inductance of the deflection coil 172. The grid of pentode 122 receives a large positive pulse through capacitor 124 from the phase inverter 118 every time the current is shifted from a positive to a negative value. This pulse is amplified and appears as a negative pulse at the plate of pentode 122. This negative pulse is coupled into the deflection coil along with the normal deflection current provided by the differentially acting current control triodes 114 and 116.

it has been demonstrated how the teachings of the present invention may be applied to a circuit which may supply current for precisely deflecting an electron beam in response to an inputsignal. Circuits of this type may be utilized in producing printed matter by electronic means from a coded input signal. Other uses of circuits of this type have been suggested. One additional field of utilization may be in the deflection circuit of an electronic color print corrector. This type of current supply circuit may be used in various applications where a current supply which precisely corresponds to an input signal must be provided. An added feature of a circuit constructed according to the teachings of this invention is that it may handle a direct current input component as well as an alternating current input component.

I claim:

1. A circuit for providing a regulated current supply for a current utilizing device precisely corresponding to an input signal comprising a current regulating device, said current regulating device being connected to said current utilizing device to govern the flow of current through said current utilizing device, a bus and means to maintain said bus at a precisely regulated predetermined potential, said current utilizing device being connected to said bus for momentarily varying the potential of said bus in response to a change in current flow through said current utilizing device, a high gain'feedback amplifier, said high gain feedback amplifier being connected to said bus to derive a control signal from said-bus in response to a change in bus potential, said high gain feedback amplifier being connected to said current regulating device for providing an amplified signal to said current regulating device, means for applying an input signal connected to said bus to momentarily change the predetermined bus potential, and said current regulating device providing means for varying the current flow through said current utilizing device to values in accordance with said input signal in response to a signal from said amplifier to restore the predetermined bus potential.

2. The combination set forth in claim 1 in combination with centering means for adjusting said values of current flow through saidcurrent utilizing device comprising a variable source of potential, said variable source of potential being connected to said high gain feedback amplifier for biasing said amplifier to provide means for adjusting the fiow of current through said utilization device to a preselected current when zero input signal is applied to said bus.

3. A circuit providing a range of precise discrete increments of current for a current utilizing device comprising a current regulating device, said current regulating device being connected to said current utilizing device to govern the flow of current through said current utilizing device, a bus and means to maintain saidbus at a predetermined substantially constant potential, said current utilizing device being connected to said bus for momentarily varying the potential of said bus in response to current flow through said current utilizing device, a high gain feedback amplifier, said high gain feedback amplifier being connected to said bus to derive a control signal from said bus in response to a change in bus potential, said high gain feedback amplifier being connected to said current regulating device .for providing an amplified signal to said current regulating device, means for providing a stepped input signal connected to said bus to momentarily vary the precisely regulated bus potential, and said current regulating device providing means for varying the current flow through said current utilizing device in discrete increments precisely corresponding to said input signal steps in response to the amplified signal from said amplifier to restore the predetermined potential being maintained on said bus.

4. A circuit providing a range of discrete increments of current for a current utilizing device comprising a current regulating device, said current regulating device being connected to said current utilizing device to govern the flow of current through said current utilizing device, a bus and means to maintain said bus at a predetermined substantially constant potential, said current utilizing device being connected to said bus for momentarily varying the potential of said bus in response to current flow through said current utilizing device, a high gain feedback amplifier, said high gain feedback amplifier being connected to said bus to derive a control signal from said bus in response to a change in bus potential, said high gain feedback amplifier being connected to said current regulating device for providing an amplified signal to said current regulating device, means for developing precise discrete increments of current being connected to said bus to momentarily vary the 10 precisely regulated bus potential, said current regulating device providing means for varying the current flow through said current utilizing device in response-to the amplified signal from said amplifier to restore the predetermined potential being maintained on said bus.

5. The combination set forth in claim 4 wherein said means for developing precise discrete increments of current is comprised of a plurality of electronic switches each in series with a precision resistor, a source of potential, each series connected electronic switch and resister being connected between said bus and said source of potential for providing to said bus a precise discrete increment of current.

'6. A circuit for providing a current supply for an electron beam deflection coil precisely corresponding to an input signal comprising a grid controlled triode, said triode having said deflection coil connected in its load circuit to govern the flow of current through said deflection coil, a bus and means to maintain said bus at a precisely regulated predetermined potential, said triode being connected to said bus for varying the potential of said bus in response to a change in current flow through said deflection coil, a high gain multistage feedback amplifier having control grids, the control grid of the first stage of said high gain feedback amplifier being connected to said bus to derive a control signal from said bus in response to a change in bus potential, said high gain feedback amplifier having its output connected to the control grid of said triode for providing an amplified signal to said triode, said bus having means for applying an input signal to momentarily change the predetermined bus potential, said grid controlled triode providing means for varying the current fiow through said current utilizing fiection coil comprising a grid controlled triode, said triode having said deflection coil connected in its load circult to govern the fiow of current through said deflection coil, a bus and means to maintain said bus at a precisely regulated predetermined potential, said triode load circuit being connected to said bus for varying the potential of said bus in response to a change in current flow through said deflection coil, a high gain feedback amplifier, said amplifier being connected to said bus to derive a control signal from said bus in response to a change in bus potential, said high gain feedback amplifier being connected to the control grid of said triode for providing an amplified signal to said triode, said bus having terminal means for applying an input signal to momentarily change the predetermined bus potential, means for selectively developing precise discrete increments of current, said current developing means being connected to said terminal means for momentarily changing the potential of said bus in discrete precise increments, and said grid controlled triode providing means for varying the current flow through said deflection coil in discrete increments pre cisely corresponding to said developed increments in response to a signal from said amplifier in order to restore the predetermined bus potential.

8. A circuit for selectively providing a. range of discrete precise increments of current varying from positive to negative values for an electron beam deflection coil comprising a pair of cascaded grid controlled triodes, a bus and means to maintain said bus at a precisely regulated predetermined potential, said deflection coil being connected to the mid point of said cascaded triodes and being connected to said bus for governing the fiow of current through said deflection coil and for varying the potential of said bus in response to a change in current flow through said deflection coil, a high gain feedback amplifier, said high gain feedback amplifier being connected to said bus to derive a control signal from said bus in response to a change in bus potential, 21 phase inverter, said high gain feedback amplifier being directly connected to the control grid of one of said cascaded triodes and being indirectly connected to the control grid of the other of said triodes through said phase inverter to provide a phase inverted signal to said triodes, said bus having terminal means for applying an input signal to momentarily change the predetermined bus potential, means for selectively developing precise discrete increments of current, said current developing means being connected to said terminal means for momentarily changing the potential of said bus, and said cascaded grid controlled triodes providing differentially acting means for varying the current flow through said deflection coil in discrete increments precisely corresponding to said developed increments in response to said phase inverted signal from said amplifier in order to restore the, predetermined bus potential.

9. The combination set forth in claim in combination with means for shifting the current flow through said deflection coil more rapidly from a positive to a negative value comprising means for developing a positive pulse every time the deflection current is shifted from a positive to a negative value, means for changing said positive pulse to a negative pulse, means for amplifying said negative pulse and means for coupling said negative pulse into said deflection coil along with the normal deflection current provided by said cascaded triodes to provide additional energy to help overcome the inductance of said deflection coil.

10. A system for providing to a utilizing device a stabilized current precisely corresponding to an input signal comprising a control means connected to regulate the current flow through said utilizing device, a bus providing a potential reference means, said bus being connected to said utilizing device to cause the potential of said bus to be a function of the current flow through said utilizing device, a feedback amplifier connected to derive an input signal from said bus in response to a change in bus potential, said feedback amplifier having its output connected to said current control means for regulating the current flow through said utilizingdevice to a predetermined stabilized value to maintain the potential of said bus at said reference potential, and an input means connected to provide a signal to said bus for momentarily varying said reference potential to cause said current utilizing device to provide a stabilized flow of current precisely corresponding to said signal to restore said bus to said reference potential.

11. A system for providing stabilized increments of current to a utilizing device in response to an input signal comprising a control means connected to regulate the current flow through said utilizing device, a bus providing a potential reference means, said bus being connected to said utilizing device to cause the potential of said bus to be a function of the current flow through said utilizing device, a feedback amplifier connected 'to derive an input signal from said bus in response to a change in bus potential, said feedback amplifier having its output connected to said current control means for regulating the current flow through said utilizing device to a precisely predetermined stabilized value in order to maintain the potential of said bus at said reference potential, and an input means connected to provide steps of current to said bus for momentarily varying said reference potential to cause said current utilizing device to provide stabilized increments of current precisely corresponding to said input steps of current to restore said bus to said reference potential.

References Cited in the file of this patent UNITED STATES PATENTS 2,214,871 Westendorp Sept. 17, 1940 2,281,572 Gage May 5, 1942 2,465,406 Taylor Mar. 29, 1949 2,474,266 Lyons June 28, 1949 2,569,204 Stratton Sept. 25, 1951 2,586,888 Varela -2 Feb. 26, 1952 2,588,659 Pond Mar. 11, 1952 2,658,163 De Cola Nov. 3, 1953 2,673,238 Dmz Mar. 23, 1954 2,674,812 Hales Apr, 13, 1954 

